1. Field of the Invention
This invention relates to packaging, and particularly to a gable-top container suitable for the packaging of liquids, having improved opening characteristics and a method and apparatus for the construction thereof.
2. Description of the Prior Art
Containers for beverages such as milk, fruit juices, and drinks are conventionally constructed from blanks of thermoplastic coated paperboard. The most widely used of such containers have a rectangular cross-sectional body surmounted by a gable-top closure incorporating an extensible pouring spout. Blanks from which the containers are constructed are divided into a plurality of panels which are adapted to form the walls and closure members. The panels are formed and separated by score lines at which the blank is folded. Particular panels are intended to be joined together in a lapped arrangement in the completed container. Typically, those panels are pressed together and heated or exposed to high frequency radiation to fuse the adjoining thermoplastic surfaces and form a generally strong seal. To finally seal the filled container, two or more panels are finally joined and sealed to form a rib along the top edge of the roof panels.
FIG. 1 illustrates an exemplary flat sheet material blank for constructing a gable-top container. The inner surface or face is shown, and it is coated with a thermoplastic such as polyethylene. The outer surface may also be similarly coated. The sheet material may include a gas impermeable layer such as aluminum foil. An appropriate pattern of score lines divides blank 1A into a plurality of panels and sub-panels which are used as walls of the container and its closure parts when the container is erected.
The central portion of blank 1A comprises four body panels 2, 3, 4, and 5, having their lower edges along bottom score line 13, and their upper edges along top score line 31. These transverse score lines are shown as extending from blank edge 6 to opposite blank edge 12 in substantially parallel relationship across the face of the blank. Vertical score lines 7, 8 and 9 transect the blank to define the lateral edges of the body panel 2, 3, 4 and 5, and other panels above the body panels. These and other score lines are not necessarily straight, but may be slightly offset in certain sectors of the blank to improve the fit of the various panels in the erected container.
In the example shown in FIG. 1, side seam flap 11 is connected to one lateral edge 10 of a body member for sealing to the edge of another body member 2 by the container sealing process. Bottom closure means 26 is shown as a group of bottom closure panels 14 through 21 attached to the body members along bottom score line 13, and extending downward therefrom. Bottom closure score lines 22 through 25 enable bottom closure panels 14, 16, and 18-21 to be folded under closure panels 15 and 17 and sealed to provide a leakproof container bottom. Such a closure means is well-known in the art. A separately formed structure may alternatively be used to close the bottom of the container. In fact, any closure means which results in a satisfactorily tight seal may be used.
The gable-top of the container is formed from a series of panels above top score line 31. First and second roof panels 28 and 30 are connected to the upper edges of the first and second side panels 3 and 5, respectively. The roof panels are oppositely disposed and when erected, converge upwardly to meet along score line 44 to form a gable roof. Connected to the upper edge of the front panel 4 is a first substantially triangular end panel 29 whose two lateral edges 35 and 36 formed by score lines extend upwardly to score line 44. Similarly, second triangular end panel 27 is connected to the upper edge of back panel 2, and has lateral edges 32 and 33 which extend upwardly to score line 44.
On each side of triangular end panel 29 is a foldback panel. First foldback panel 41 is connected to triangular end panel 29 along edge 35, and to first roof wing panel 40 along score line 8. Panel 41 has a score line 44 as its upper edge. Similarly, second foldback panel 42 is connected to triangular end panel 29 along edge 36, and to second roof wing panel 43 along score line 9. It has score line 44 as its upper edge.
Similarly, third and fourth foldback panels 39 and 38 are connected to triangular end panel 27 along lateral edges 33 and 32, respectively. The third foldback panel 39 is attached to the first roof panel 28 along score line 7, and the fourth foldback panel 38 is connected to the second roof panel 30 by side seam flap 11 when the container is erected.
Attached to the upper edge of each foldback panel 38, 39, 41 and 42 along score line 44 is a gable rib panel 45, 46, 50 and 52, respectively. Similarly, attached to the upper edge of first and second roof panels 28 and 30 are first and second roof rib panels 48 and 54, respectively. First and second gable rib panels 50 and 52 are connected to each other at a common score line 51, and third and fourth gable rib panels 46 and 45 are connected to each other at common score line 47. The uppermost end 51A of line 51 is the tip of the pouring spout of the erected container. Alternatively, if a gable-top container does not include first and second gable rib panels the tip of the pouring spout is formed by the uppermost end of the first triangular end panel 29, where it connects with the first and second fold back panels.
First gable rib panel 50 is connected to first roof rib panel 48 at score line 8, and second gable rib panel 52 is connected to second roof rib panel 54 at score line 9.
First roof wing panel 40 comprises a triangular portion of first roof panel 28 defined by score lines 34, 44 and 8, and is adjacent first foldback panel 41. Second roof wing panel 43 comprises a triangular portion of second roof panel 30 defined by score lines 37, 44 and 9 and is adjacent second foldback panel 42. These roof wing panels are more or less coextensive with the adjacent foldback panel when the erected container is closed.
A first upper rib panel 49 is connected to the upper edge of the first roof rib panel 48. Likewise, a second upper rib panel 55 is connected to the upper edge of the second roof rib panel 54. The score lines 60 and 61 separate the upper rib panels from the adjacent roof rib panels, and are substantially continuous with the free upper edge 53 of the first and second gable rib panels 50 and 52. The latter panels serve as lips of the pouring spout of the erected container. However, the first and second upper rib panels are primarily provided to stiffen and strengthen the top of a sealed gable-top container. The presence of the first and the second upper rib panels is detrimental during the opening of a sealed gable-top container.
The score lines may be applied to blank 1A before or after the thermoplastic coating is applied to the blank. The score lines may be applied to either surface or both surfaces of the blank. For purposes of clearer delineation of the various panels, score lines are shown in the drawings on either or both of the inner and outer surfaces of the blank and container.
Containers of this type are opened for access to the contents by a two-step toggle action process. First, the gable edges of the roof panels at the front of the container are pushed outward and upward toward the rear of the container by thumb pressure, breaking the seal between the outside surfaces of the two lip panels, and breaking the seal in the rib panels surmounting the roof above the pouring spout. The gable edges are forced backward past the point at which the lip panels are joined, to nearly touch the roof panels.
Second, the gable edges are pushed forward and towards each other. The forces are communicated through spout panels to the tip of the pouring spout, breaking the seal between the lip panels and the underside of the roof panels and snapping the spout outward to a pouring position.
In early models of gable-top containers, the panels comprising the lips of the pouring spout were bonded to the underside of the roof panels. The resulting sealed spout was difficult to open, generally requiring insertion of a tool behind the lips to separate them from the roof underside. The cardstock panels often tore or delaminated, producing an unsightly and unsanitary container. In those cases where an adhesive was applied to only those panels which were to be joined, it was simple to eliminate adhesive from the spout panels to reduce the forces required to open the spout. The resulting container, of course, was not effectively sealed and was subject to leakage.
An improvement in gable-top containers to provide a hermetic seal for an extended shelf life package consisted of coating the inner surface of the container blank with a foil and an overcovering layer of thermoplastic such as polyethylene. The panels to be sealed are bonded by heating the thermoplastic surface coatings to a softening or melting temperature, compressing the panels together and cooling. The use of thermoplastic coatings or foil adds some stiffness to the panels, and the container is made resistant to wicking by liquids. However, the strong bonding of the lip panels results in buckling, tearing and delamination of the cardstock upon opening the seal. Thus, the spout is difficult to open, and the opened panels are unappealing in appearance.
As used in the food packaging industry, the term hermetic refers to a container designed and intended to be secure against the entry of oxygen which degrades flavor. The term is also used to designate containers used for aseptic filling and storage, i.e. containers secure against the entry of microorganisms. The hermetic barrier of such cartons typically comprises an aluminum or other barrier film coating the inner surface, overcovered with a thermoplastic such as polyethylene. The carton wall thickness is thus increased, resulting in larger channels where the edges of overlying panels have a stepped relationship in the gable rib area, increasing the chance for leakage.
Attempts to provide an easily opened spout seal have included: (a) perforations in the spout panels which tear open to expose pouring lips; (b) improved control of the sealing temperature; (c) the use of added scoreline patterns to concentrate the opening forces; and (d) the use of anti-adhesion agents, i.e. abhesives, to reduce the required opening forces.
The use of perforations in the spout panels has generally been unsatisfactory. Such perforations produce a spout of reduced size. The perforations are considered by some to be a weak point in the carton, prone to develop leaks. This type of carton spout requires external forces such as thumbnail pressure to open, and this procedure is considered unsanitary. The carton cannot be effectively closed, once opened, and shaking of the carton results in spillage.
Likewise, efforts to reduce temperature variations in the sealing process have not produced a satisfactory hermetic sealing gable-top container. Because of the narrow acceptable temperature range for obtaining the desired adhesion, sealing variations persist in spite of improved temperature control. Moreover, the required opening forces generally exceed the panel strength, even where minimal sealing is achieved.
The use of novel scoreline patterns generally has not overcome the strong sealing forces of well-sealed spouts and buckling of the spout panels is common.
One method for preventing the difficulty in opening the completely bonded lip panels of polyethylene coated gable-top containers is shown in Crawford et al, U.S. Pat. No. 3,116,002. In this reference, a thin coating of a high molecular weight organo-siloxane gum is applied to the lip panels as an abhesive, that is, to prevent permanent adhesion to the panels in contact with the lip panels.
Egleston et al, U.S. Pat. No. 3,270,940 discloses the use of an anti-adhesive composition applied to both the outside and inside surfaces of the pouring lip of a gable-top container. Abhesive agents disclosed include cellulose plastic laminated to polyethylene, the latter heat-bondable to the polyethylene surface of the cardstock blank.
The release properties of abhesives are generally affected by the heat sealing parameters and are inconsistent. Containers designed for hermetic use and having adhesives in the spout sealing area often require opening forces greater than the wall strength of the panels, and the spout panels buckle during the opening process.
European patent application No. 0,331,792, entitled "Easy Open Gable Top Carton" represents another approach to control the opening force for gable-top containers. Conventional gable-top container sealing apparatus and methods employ a pair of opposed sealing bars or jaws positioned adjacent the exterior of the overlapping pouring spout panels. Each sealing jaw includes a sealing surface for application to the exposed surfaces of the overlapping pouring spout panels. Means are provided for heating the container panels to a desired temperature sufficient for sealing of facing surfaces of the pouring spout panels of the gable-top container. Usually, such means takes the form of streams of heated air directed against the panels of the container to be sealed, in a manner known in the art, and thus will not be discussed herein further.
Means are also provided for movement of the sealing jaws from a spaced apart position to opposed positions in compressive contact with the panels to be sealed during the sealing of the gable-top container. The application of heat and the pressure of the sealing jaws will seal the gable-top container, as previously described. Such sealing jaws are known in the art and the mechanism for moving the sealing jaws against the gable-top container panels and compressing the panels are also known in the art and will not be discussed in greater detail hereinafter.
The above mentioned European patent application no. 0,331,792 provides a pair of sealing jaws having aligned recesses. The recesses are positioned to apply a reduced level of sealing force or no sealing force to aligned potions of the overlapping panels of the end panels and side panels forming the gable top of the container. In the illustrated embodiment of a gable-top container blank, the corresponding panels are the first and the second roof rib panels 48, 54 and the first and the second gable rib panels 50, 52. The unsealed or lightly sealed areas on the overlapping panels are intended to reduce the opening force of the sealed container. However, even the arrangement in European patent application no. 0,331,792 does not adequately reduce the opening force to an acceptable level for gable-top containers including panels corresponding to the first and second upper rib panels 49, 55. Specifically, the arrangement described in European patent application no. 0,331,792 fails to recognize that a large portion of the opening force involves the separation of the first and second upper rib panels from each other and the subsequent buckling and deformation of these panels during the first phase of the opening process.
Moreover, recently gable-top containers have been developed for extended storage of food stuffs. Such designs have included tougher (e.g. thicker material or laminates having additional layers) laminates. Such gable-top containers, as illustrated in U.S. Pat. No. 4,787,507, drastically increase the effort required to open the container to an unacceptically high level, even for approaches as described in European patent application no. 0,331,792.
Thus, the limitations of conventional gable-top containers described herein are rendered more acute as the integrity of gable-top containers having first and second upper rib panels is increased. None of the existing gable-top container designs provide a secure seal and yet successfully facilitate easy and quick opening of a gable-top container including first and second upper rib panels.